Method for reducing detector noise in a chromatography system

Abstract

A controller (30) based chromatography system (2) especially designed for flexibility of operation with ease of use and an icon based control panel (32), has a number of function panels (34), each having a function key (36), one or more indicator indicia (40) in the form of icons, letters or numbers, and associated indicator lights (38). A switching valve (4) is used to provide a mixture of two or more solvents (6, 8) to a peristaltic pump (12). The cyclic nature of the pump and mixer can create a resonant condition resulting in poor quality information from the UV monitor (20). The system minimizes this by the judicious selection of the total cycle time T for the switching valve. This can be done using a random number manipulated in a manner to come up with each time T. Alternatively, an irrational number is combined with the pulsation frequency of the pump to create each time T. A valve driver circuit (170) used with a valve (172) of the type which requires a higher voltage switching signal (174) and lower voltage sustaining signal (176). The system permits the user to use three different nominal flow rate calibrations for peristaltic pumps using tubing having three different diameters (82, 84, 86). In addition to the precalibrated settings, the system can be user calibrated when desired.

What is claimed is: 
     
       1. A method for reducing detector noise in a chromatography system of type including a switching valve, a cyclic pump, a column and a detector, the switching valve coupling first and second liquids to the pump for first and second time segment fractions X, Y out of a time period T according to the desired proportions of the first and second liquids, the method comprising: choosing a range for T between a minimum time period T(min) and a maximum time period T(max);   selecting an irrational number IN;   determining the current pulsation frequency P(new) of the pump;   combining IN and P(new) to create a second irrational number IN(new) in a manner such that IN(new) is a number of time units;   multiplying IN(new) by an integer I(new) to create a time period T(new) between T(min) and T(max);   operating the switching valve using T(new) to connect the first liquid to the pump for a first time period equal to T(new) * X and to connect the second liquid to the pump for a second time period equal to T(new) * Y; and   repeating the determining, combining, multiplying and operating steps while the pump is operating to pump a mixture of the first and second liquids through the system.   
     
     
       2. The method of claim 1 wherein the choosing step is carried out using T(min equal to 2 second and T(max) equal to 5 seconds. 
     
     
       3. The method of claim 1 wherein the selecting step is carried out by selecting the square root of 2 as IN. 
     
     
       4. The method of claim 1 wherein the determining step is carried out using the following formula when the pump is a peristalic pump:   P(new)=N * S(new)     where:   N=the number of rollers of the peristalic pump,   S(new)=the current rotational speed of the pump in revolutions per second; and   P(new)=number of pulses per second at S(new).   
     
     
       5. The method of claim 1 wherein the operating step the first liquid is connected to the pump continuously during the first time period.